1. Field of the Invention
The present invention relates to improvement in rolling metal rods, particularly, steel rods, to produce steel wires. According to the present invention it is possible to produce wire of various diameters staring from a rod of one diameter without change rollers.
2. Description of the Prior Art
Production of wires of diameters in the range of several millimeters to twenty millimeters by wire rolling of steel rods has been usually carried out by using a material round rod having a diameter of 20 mm or so supplied from rough rolling step, rolling the material in a block mill equipped with eight rollers as intermediate rolling mill, and then, finish rolling the wire with a sizing mill equipped with sets of two rollers. Structure of the rolling mill is as shown in FIG. 1.
There is strict requirement to sizes of steel wires depending on the ultimate use thereof. For example, in the range of diameter of 5-10 mm, products having the sizes of each 0.5 mm increase are required, and in the range of diameter 10-20 mm, those having the sizes of each 1.0 mm increase are required. Recently, a demand has arisen for hot rolled wire products of various calibres which precisely conform with the required cross-section.
A conventional method for satisfying this demand is the sequence of the following rolling steps illustrated in FIG. 2.
In the range of "very fine" (diameters 5.5, 6.0 and 6.5 mm) wire rolling starts from a round rod of diameter 16.4 mm supplied from rough intermediate line. The rod material is first rolled by a block mill (F1-F8) having the first roller group to diameter 6.5 mm, then the rolled material is passed to the sizing mill to be rolled by both the front group of the rollers and the rear group of the rollers (5.5 mm), or by only the front group of the rollers (6.0 mm).
In the range of "fine" (diameters 7.0, 7.5 and 8.0 mm) a round rod of diameter 20.5 mm is used as the material from the rough intermediate line. In order to switch to this range, it is necessary to shut down the line to carry out roller change of all the stands, and form a block mill (F1-F8) having the second roller group. After rolling the round rod material of diameter 20.5 mm to 8.4 mm, the rolled material is passed to the sizing mill so that it may be rolled by both the front group and the rear group (7.0 mm), by only the front group (7.5 mm), or by only the front group of changed rollers.
In the range of "intermediate fine" (diameters 8.5, 9.0, 9.5 and 10.0 mm) as shown in FIG. 3, rolling also starts from the same round rod material of diameter 20.5 mm as above. The round rod material is rolled by a part (F1-F6) of the block mill having the second group of rollers to diameter 10.5 mm. For this purpose it is also necessary, after shutting down the line, to remove the rollers of F7 and F8 stands, and to install a dummy guide. The rolled material coming out of the dummy guide is passed to the sizing mill so as to use both the front and the rear groups of rollers (8.5 mm), only the front group (9.5 mm), or with changed rollers, only the front and rear group (9.0 mm), or only the rear group (10.0 mm).
In the range of "intermediate bold" (diameters 11.0 and 12.0 mm), the rolling also starts from the round rod material of diameter 20.5 mm. The material is rolled by a part (F1-F4) of the block mill having the second group of rollers to diameter 13.1 mm. Also in this case the rollers of F5 and F6 stands are removed and replaced with a dummy guide. The rolled material of diameter 13.1 mm is passed to the sizing mill, and rolled by both the front group and the rear group of the rollers (11.0 mm), or by only the front group (12.0 mm).
With reference to FIG. 4, production of wires in the thickness range of "bold" (diameters 13.0, 14.0, 15.0 and 16.0 mm) starts also from the round rod of diameter 20.5 mm, which is first rolled by a part (F1-F2) of the second group of rollers to diameter 16.4 mm. Block mill rollers of F3 and F4 stands are also removed. The rolled material of diameter 16.4 mm is passed to the sizing mill and rolled by both the front and the rear group of the rollers (13.0 mm), or by only the rear group (15.0 mm). Alternatively, the rolled material is rolled, after changing rollers, by both the front and rear groups (14.0 mm) or by only the rear group (16.0 mm).
Wires in the thickness range of "very bold" (diameters 17.0, 18.0 and 19.0 mm) are produced, also starting from the round rod material of diameter 20.5 mm, by not using the block mill but directly using the sizing mill. Both the front and the rear groups of the rollers are used (17.0 mm), only the front group is used (19.0 mm) or both the front and the rear groups with changed rollers are used (18.0 mm).
In FIG. 2 to FIG. 4 demarcation with lines indicates that rollers are used in the areas and that no roller is used in the other area. The round forms illustrate that calivers of the rollers (consequently, the sections of the rolled material coming therefrom) are round, and the oval form, oval sections of the rolled materials. The numerical figures annexed to the round forms show the diameters of the material coming out of the round caliber rollers.
Change of sizing mill rollers is easy, and even the whole roll stands can be changed. However, because ratios of rotating speeds of the rollers are fixed in the block mills, it is necessary to use continued stands. Also, because the roller axes are set fixedly to the pass line, it is necessary to carry out roller changing after interrupting the rolling operation in which the block mill is involved. In regard to the above described examples, in the thickness ranges of "very fine" and "fine" entire stands of the block mill are changed. Changes between the thickness range of "fine" and "intermediate fine", "intermediate fine" and "medium bold", and "medium bold" and "bold" necessitate mounting and demounting of the rear group rollers.
Thus, attempt to produce steel wires of various sizes by the conventional technology requires troublesome preliminary work for roller change, and this lowers efficiency of production. If, however, large scale production of one size at once is done for the purpose of avoiding the above problems, then, excessive stock of the wire product must be kept in inventory. Additional problems such as scratching during handling and transporting and rusting during storage may occur.
The object of the present invention is to solve the above discussed problems relating to wire rolling, and to provide a method of rolling which enables production of wire products having various diameters from a round rod of one diameter without change of block mill rollers, is a lengthy and laborious process. The invention also provides a rolling mill for carrying out the rolling method.